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In 1976 the National Council for Civil Liberties, the respectable (and responsible) pressure group now known as Liberty, made a submission to parliament's criminal law revision committee. It caused barely a ripple. "Childhood sexual experiences, willingly engaged in with an adult," it read, "result in no identifiable damage … The real need is a change in the attitude which assumes that all cases of paedophilia result in lasting damage."

It is difficult today, after the public firestorm unleashed by revelations about Jimmy Savile and the host of child abuse allegations they have triggered, to imagine any mainstream group making anything like such a claim. But if it is shocking to realise how dramatically attitudes to paedophilia have changed in just three decades, it is even more surprising to discover how little agreement there is even now among those who are considered experts on the subject.

A liberal professor of psychology who studied in the late 1970s will see things very differently from someone working in child protection, or with convicted sex offenders. There is, astonishingly, not even a full academic consensus on whether consensual paedophilic relations necessarily cause harm.